One method for protecting metals against corrosion is to connect the metal directly to a "sacrificial anode". This is the method used to protect pipelines and ships hulls. Which of the following metals would you consider the best candidate for a sacrificial anode for a ship's hull? The hull is steel (which is mostly iron).

Electrochemistry |

Oxidation / Reduction |

Metals

Equilibrium : CommonIonEffect (9 Variations)
The molar solubility of lead(II) fluoride (PbF2) is
2.1 x 10-3 mol/L in pure water at 25oC. What is the molar solubility of lead(II) fluoride in 0.10 M NaF at 25oC? (Assume that the only relevant reaction is the solubility-product equilibrium.)

Equilibrium |

Chemometrics

Equilibrium : ConcFromKsp (8 Variations)
The Ksp of BaF2 is
1.7 x 10-6 mol/L in water at 25oC. What is the concentration of barium ions in equilibrium with solid barium fluoride? (Assume that the only relevant reaction is the solubility-product equilibrium.)

Equilibrium : KspSaturation (12 Variations)
Zn(OH)2 has a Ksp of 4.5 x 10-17. If you have a solution of Zn(OH)2 that has a hydroxide ion concentration equal to 4.6 x 10-6 mol/L, the solution is ... (Assume that the only relevant reaction is the solubility-product equilibrium.)

Gases : GasRxnVolumes (10 Variations)
A gas phase reaction takes place in a syringe at a constant temperature and pressure. If the initial volume before reaction is 30 mL and the final volume after the reaction is complete is 15 mL, which of the following reactions took place? (Note: You can assume that you start with stoichiometric amounts of the reactants, the reaction goes to completion and that the gases behave ideally.)

Gases : GasLaws (2 Variations)
Note: This is a calculation type question. If you exit the quiz without submitting it and you do not save an answer before exiting the quiz, the values in the question may change when you enter the quiz again.

You purchase a propane tank that can hold gas safely up to a pressure of {x} atm. When the tank contains 100. grams of propane at {y}°C, the gas exerts a pressure of {z}atm. What is the highest temperature to which the propane can be heated safely? (Report your answer in Kelvins.)

Gases |

Chemometrics

Gases : IdealGasMolarMass (10 Variations)
A sealed flask contains 3.1 L of a gas at 2.4 atm and 22.7oC. If the density of the gas is 9.7 g/L, what is its molar mass? (You can assume that the gas behaves ideally.)

Gases |

Chemometrics

Gases : IDGasFromVelocity (8 Variations)
The following are graphs of molecular velocities versus the relative number of molecules for argon, chlorine, methane and xenon at 300K. Which graph is for argon?

Gases : OzoneMolcsFromppm (10 Variations)
Although ozone is an important component of the upper atmosphere, long-term exposure to ozone in the air we breathe can cause inflammation of the lung, impairment of lung defense mechanisms, and irreversible changes in lung structure. The EPA has set an 8 hour limit for ozone of 0.08 ppm as an air quality standard for cities. At the EPA limit, how many ozone molecules are present in 5.0 liters of air at 25oC and 0.967 atm? (Hint: assume that air is an ideal gas and calculate the total number of molecules there are in 5.0 L. Then use the definition of ppm.)

Gases : VolGasReactInTorch (10 Variations)
Oxyacetylene torches used in high-temperature welding use a combination of oxygen and acetylene. The combustion of acetylene (C2H2) occurs in these torches. What volume of oxygen is needed to react with 250 mL of acetylene?

Gases |

Stoichiometry

Kinetics : ConcVsTimeGraph (8 Variations)
The following graph shows the change in concentration as a function of time for the reaction:
2NO2(g) + F2(g) 2NO2F(g)
What do each of the curves A, B, and C represent?

Kinetics

Kinetics : Enzyme (7 Variations)
Trypsin assists in digestion by breaking proteins down into smaller peptides. However, this process is not as efficient in the presence of fluorophosphates. Identify the role of each of these components.

(1) Based on the units of the rate constant, what is the order of the reaction? {1:MULTICHOICE:zero-order#No, that is not correct.~=first-order#Correct!~second-order#No, that is not correct.~third-order#No, that is not correct.}

(2) What is the concentration of CH3CN after 0.20 minutes of reaction if the initial concentration is 0.10 M? {1:NUMERICAL:=4e-4:1e-5#Correct!~%50%4e-4:5e-5#Close, but not quite.}(Do not include units!)

Using the graph below, calculate the rate constant for this reaction at 40.0oC.

Kinetics |

Chemometrics

Kinetics : ArrheniusTemp (3 Variations)
The activation energy for the isomerization of cyclopropane to propene is 274 kJ/mol. By what factor does the rate of reaction increase as the temperature rises from 500oC to 550oC assuming all else remains constant? (R = 8.314 J/mol k)

Hint: This is asking for the ratio of rates which is proportional to the ratio of the rate constants, all else being equal.

Catalytic converters are used in automobiles to convert pollutants in engine emissions to benign products. Catalytic converters in today's automobiles are made of a porous ceramic brick that has been coated with catalysts, additives, stabilizers, and support materials. Corning has developed bricks that have very thin-walled channels with 600 channels per square inch. Which of the following research goals did they target?

Reactions : AcidBaseRxns (20 Variations)In order to answer the following questions, write the net ionic equation for the reaction between equal volumes of 0.10 M solutions of the following acid and base:

KOH(aq) + HBr(aq)

What are the reaction products? Does the reaction yield an acidic, basic, or neutral aqueous solution?

Solutions : ConvertConcUnits (10 Variations)The maximum concentration of arsenic in drinking water that is allowed by the EPA is 0.050 mg/L. Express this as a weight percent. (You can assume the density of the water solution is 1.0g/mL.)

Solutions / Solvents |

Nomenclature / Units / Symbols |

Chemometrics

Solutions : FreezePtDepression (20 Variations)It takes 6.86 kg of ethylene glycol (antifreeze) to decrease the freezing point of 6.50 kg of water to -25.0oF (-31.7oC). How much sodium chloride (NaCl) would it take to decrease the freezing point of 6.50 kg of water to -25.0oF? (Assuming all the salt will dissolve in that amount of water.)

Solutions : ReverseOsmosis (20 Variations)You are given a water sample that contains ammonium chloride (NH4Cl). You determine the concentration of the salt to be 0.500 M and decide to purify the water using reverse osmosis. What is the minimum pressure that must be applied at 30.0oC to force the water through the membrane?

Solutions : SolnPrepByDilution (10 Variations)For the analysis of trace metals it is necessary to prepare solutions of very low concentrations from a stock solution of higher concentration using a micropipet and a volumetric flask. What volume of a 0.0010 M solution of Zn(NO3)2 (aq) would be required to prepare a 5.0 nM solution of Zn2+ in a 250mL flask?

Solutions : WtPercentToMolarity (4 Variations)
A common concentration unit used commercially is percent weight per volume (%W/V) which is the number of grams of solute in 100 mL of solution. A bottle of vinegar contains 5 %W/V acetic acid (CH3COOH). What is the molar concentration of acetic acid in the vinegar?

Stoichiometry : CombustionAnalysis (10 Variations)
While working in the lab, you find a bottle of white powder labeled
"analgesic compound #5". Since the original investigator neglected
to record the identity of the substance, you decide to perform a
combustion analysis to identify the compound. You have a 65.7 g
sample that when burned produces 182 g CO2 and 51.7 g
H2O. What is the formula of this compound? (The compound
only consists of C,H, and O.)

Stoichiometry : ExplainYldError (4 Variations)
Your TA gives you an aqueous solution containing an unknown quantity of AgNO3(aq) and an unknown quantity of Mg(NO3)2(aq). You are asked to determine the molarity of Ag+ in the solution. You add HCl(aq) to your unknown to precipitate the silver as AgCl(s), then filter out the precipitate, dry it, weigh it, and calculate the concentration of silver ion. However, your TA tells you that your calculated value of [Ag+(aq)] is lower than the actual value. Which of the following could account for your answer being too low? There may be more than one correct answer.

Stoichiometry |

Reactions |

Chemometrics

Stoichiometry : FormulaFromComp (8 Variations)
Lactic acid is the substance that makes your muscles burn when you've been exercising hard. Lactic acid is composed of 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by weight. If it has a molar mass of 90 g/mol, what is its molecular formula?

Stoichiometry : PrecipYield (3 Variations)
In a laboratory experiment to determine accurately the amount of barium in solution, aqueous sulfuric acid was added to the solution to precipitate barium sulfate, which was then filtered and weighed. In this experiment it is MOST important that ...

Thermochemistry : SystemSurrExoEndo (4 Variations)
Sulfuric acid is added to water in a beaker and the resulting solution is much warmer than either the water or acid was initially.
Identify the following items as being part of the system or the surroundings, and indicate whether the process is exothermic or endothermic.

Calorimetry / Thermochemistry

Thermochemistry : BombCalorimeter (4 Variations)
Stearic acid (CH3(CH2)16CO2H) is a fatty acid, the part of fat that stores most of the energy. 1.00 g of stearic acid was burned in a bomb calorimeter. The bomb had a heat capacity of 652 J/oC and a 500. g water reservoir. If the temperature rose from 25.0 to 39.3 oC, how much heat was released when the stearic acid was burned?

Thermochemistry : CoffeeCupCalorimeter (2 Variations)
A block of copper is heated to {x} °C and then is dropped into a coffee cup calorimeter containing {y} g of water at 25.0 °C. The final temperature of the system is 45.1 °C. What is the mass of the copper block to the nearest gram? (Assume all heat is transferred to the water). Write your answer in the box, and do NOT include units.

Specific heat capacity of copper = 0.383 J/(g*°C)

Specific heat capacity of water = 4.18 J/(g*°C)

Calorimetry / Thermochemistry |

Chemometrics

Thermochemistry : FuelAmpWattHeat (4 Variations)
Gasoline has an enthalpy of combustion of approximately 24000 kJ/gallon. When gasoline burns in an automobile engine, approximately 30% of the energy released is used to produce mechanical work. The remainder is lost as heat transfer to the engine's cooling system and eventually the atmosphere. As a start on estimating how much heat transfer is required, calculate what mass of water could be heated from 25 to 100oC by the combustion of 1.0 gallon of gasoline in an automobile.

Consider the graph above. Which of these substances has the highest specific heat capacity?

Calorimetry / Thermochemistry |

Heat Capacity

Thermochemistry : HeatCapacityLiq (4 Variations)
100 g of water (c=4.184 J/g.oC), 100 g of ethanol (c=2.46 J/g.oC), 100 g of carbon tetrachloride (c=0.861 J/g.oC), and 100 g of ethylene glycol (c=2.42 J/g.oC) at 50oC were each placed into a separate coffee cup calorimeter and the temperature recorded. The temperature of the surroundings was 20oC. After one hour the temperature of which substance would have changed by the largest amount? Assume that the rate of heat transfer from the coffee cup to the surroundings was the same in each case.